PS Authorization Check (CJ20N)

I am implementing 'authorization check' to projects and WBS elements. I found the enhancement CNEX0002 and everything worked fine for all PS transactions, except for CJ20N.

The implementation is to not allow changes for projects (and all it's WBS element) which I have no authorization. So we can see them (in gray color), but cannot change.

The problem is when we open a Project or WBS element at CJ20N. If I have no authorization to change them, the objects comes with no possibility for inputting data, but when we try to create an activity, it works and should not work.